Generally, fine metal burrs or cracks remain on fracture faces in a manufacturing process for a metal component, and a removing process for these burrs or cracks is carried out by barrel polishing.
However, in this process, barrel media (ceramic in general) are stuck into a material surface and left thereon as they are.
Further, in a product with a simple shape, cracks or fracture faces are smoothed on some level through the barrel polishing. However, in a product with a complicated shape, it is impossible to appropriately hit an entire surface with barrel media. This causes unevenness in polishing so that cracks or incompletely-polished fracture faces may remain.
If a product in such a condition is used for an actual product, remaining barrel media or materials themselves drop at the time of assembly of components including the product or after assembly of the finished product, to exert a functional influence on the peripheral devices.
To prevent such dropping, an electroless nickel phosphorus plating process or other coating process is carried out to completely coat a surface of a product. It has a profound effect.
However, the electroless nickel phosphorus plating process or other coating process has an advantage in quality whereas it invariably involves a disadvantage of high cost.
Further, a product may need to be welded, and the product to which the electroless nickel phosphorus plating process or other coating process is carried out causes insufficient welding strength. This involves a problem that a process for welding and coating cannot be realized.
On the other hand, there is a method of manufacturing an iron-based component, which heat-treats a component in a reducing atmosphere after barrel polishing to reduce oxides remaining on a surface and leave iron thereon and keeps diffusion temperature to diffuse iron and flakes of a base material into the base material, thereby to reduce the number of particles remaining on the surface.
However, the barrel polishing leaves irregularities or scratches at the micro level on the surface, and there is a limit on a smoothness of fracture faces at a punched portion. The subsequent heat treatment cannot form a pseudo-plated layer, so that it cannot obtain quality equivalent to the plating or other coating process.
This involves a problem that contaminants (inclusions) spattering from the outside are likely to adhere to even the surface processed by the heat treatment after the barrel polishing.
PATENT DOCUMENT 1: JP Patent No. 3563037